JP2011008087A - Developing device and image forming apparatus - Google Patents

Abstract

An afterimage can be prevented from being formed on a medium, and image quality can be improved.
A first roller 161, a second roller 162, a third roller 163, and a developing belt 164 are provided. The developing belt 164 is brought into contact with the image carrier at the facing portion D2 between the first and second rollers 161 and 162 and with the developer supply member at the contact portion between the first and third rollers 161 and 163. . In the facing portion D2, the developer on the developing belt 164 is attached to the image carrier. In the contact portion, the developer is supplied to the developing belt 164, and the developer is collected on the developer supply member. The developer remaining on the developing belt 164 does not adhere to the image carrier as it is in the next development process.
[Selection] Figure 1

Description

  The present invention relates to a developing device and an image forming apparatus.

  Conventionally, in an image forming apparatus such as a printer, a copying machine, a facsimile machine, and a multifunction machine using an electrophotographic method, for example, a printer, processes such as charging, exposure, development, transfer, cleaning, and static elimination are performed on the photosensitive drum. The toner image formed on the photosensitive drum around the photosensitive drum is transferred to a sheet as a medium and fixed.

  By the way, a printer provided with a belt-type developing device for performing a developing process is provided. The developing device supplies toner to the electrostatic latent image formed on the photosensitive drum to form a toner image, supplies the toner to the developing belt, and is not used for development. A developing roller is provided for scraping off the toner remaining on the belt. A voltage for supplying toner to the developing belt is applied to the developing roller (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 7-64445

  However, in the conventional developing device, an electric field is formed by the voltage applied to the developing roller so that the charged toner adheres to the developing belt, and the toner remaining on the developing belt is sufficiently removed. Can not be scraped off. Therefore, the toner remaining on the developing belt in the previous development process may adhere to the photosensitive drum as it is in the next development process. In this case, an afterimage is formed on the paper and the image quality is lowered. End up.

  The present invention provides a developing device and an image forming apparatus capable of solving the problems of the conventional developing device, preventing an afterimage from being formed on a medium, and improving image quality. With the goal.

  For this purpose, in the developing device of the present invention, the first roller, the second roller, the third roller, and the first to third rollers are stretched, and the first to third rollers A developing belt that is caused to travel as rotation is transmitted to the predetermined roller.

  The developing belt is opposed to the image carrier at a facing portion set at a predetermined position between the first and second rollers, and is set at a predetermined position between the first and third rollers. The contact portion is brought into contact with the developer supply member.

  Further, the developer on the developing belt is adhered to the image carrier at the facing portion.

  In the contact portion, the developer is supplied from the developer supply member to the development belt, and the developer is collected from the development belt to the developer supply member.

  According to the present invention, in the developing device, the first roller, the second roller, the third roller, and the first to third rollers are stretched, and the first to third rollers A developing belt that is caused to travel as rotation is transmitted to the predetermined roller.

  The developing belt is opposed to the image carrier at a facing portion set at a predetermined position between the first and second rollers, and is set at a predetermined position between the first and third rollers. The contact portion is brought into contact with the developer supply member.

  Further, the developer on the developing belt is adhered to the image carrier at the facing portion.

  In the contact portion, the developer is supplied from the developer supply member to the development belt, and the developer is collected from the development belt to the developer supply member.

  In this case, the developer on the developing belt is adhered to the image carrier at the facing portion, and the developer is supplied from the developer supplying member to the developing belt at the contact portion, and the developer supplying member from the developing belt. Thus, the developer remaining on the developing belt in the previous development process does not adhere to the image carrier as it is in the next development process.

  Therefore, an afterimage can be prevented from being formed on the medium, and the image quality can be improved.

It is a figure explaining operation | movement of the developing device in the 1st Embodiment of this invention. 1 is a conceptual diagram of a printer according to a first embodiment of the present invention. FIG. 2 is a conceptual diagram of an image forming unit in the first embodiment of the present invention. FIG. 6 is a diagram illustrating a relationship between a distance from a contact portion and a potential formed on the developing belt in the first embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In this case, a printer as an image forming apparatus will be described.

  FIG. 1 is a diagram for explaining the operation of the developing device in the first embodiment of the present invention, FIG. 2 is a conceptual diagram of the printer in the first embodiment of the present invention, and FIG. 3 is the first embodiment of the present invention. It is a conceptual diagram of the image formation part in the form.

  As shown in the figure, in the printer, image forming portions Bk, Y, M, and C for forming an image for each toner 14 as a developer of each color of black, yellow, magenta, and cyan are disposed. Each of the image forming units Bk, Y, M, and C includes an image forming unit 15, an LED head 23 serving as an exposure device and a transfer roller 22 serving as a transfer member, which are disposed corresponding to each image forming unit 15. A transfer unit 21 is disposed below each of the image forming portions Bk, Y, M, and C.

  The image forming unit 15 includes an image forming unit main body 15a, and a toner cartridge 13 as a developer containing portion that is detachably disposed on the image forming unit main body 15a and as a developer cartridge. The toner 14 is accommodated in the toner cartridge 13.

  The image forming unit main body 15a is formed in a drum shape, and a photosensitive drum 11 as an image carrier that carries an electrostatic latent image as a latent image. Around the photosensitive drum 11, the photosensitive drum 11 is provided. As a developing device that develops an electrostatic latent image formed on the surface of the photosensitive drum 11 and forms a toner image as a developer image. A developing unit 20 and a cleaning blade 19 as a cleaning member are provided.

  The photoconductor drum 11 includes a photoconductor made of an organic optical semiconductor as a surface layer, and is rotated in the direction of arrow a. The charging roller 12 applies a charge to the photoconductor of the photoconductor drum 11, and the photoconductor drum 11 The surface is uniformly charged to -600 [V]. For this purpose, a negative polarity voltage is applied to the charging roller 12. Further, in order to reduce wear of the photosensitive drum 11, the charging roller 12 is rotated with the photosensitive drum 11.

  The LED head 23 uses an LED element as a light source and forms an electrostatic latent image on the surface of the photosensitive drum 11. The surface of the photosensitive drum 11 charged to −600 [V] by the charging roller 12 is exposed by the LED head 23, and the potential of the surface on which the electrostatic latent image is formed is set to −50 [V]. Note that a laser may be used in place of the LED head 23.

  The transfer unit 21 is stretched by a driving roller 25a as a driving roller, an idle roller 25b as a driven roller, and the driving roller 25a and the idle roller 25b. A transfer belt 24 as a belt member disposed in contact with the photosensitive drum 11, and the transfer roller 22 disposed to face each photosensitive drum 11 through the transfer belt 24. Each of the transfer rollers 22 sequentially superimposes and transfers the toner images of the respective colors on the photosensitive drums 11 on a sheet (not shown) as a medium conveyed by the transfer belt 24, thereby forming a color toner image. The toner 14 remaining on the photosensitive drum 11 after the transfer is scraped off and removed by the cleaning blade 19.

  Also, below the transfer unit 21, a paper feed cassette 31 is disposed as a medium storage unit for storing paper, and the paper feed cassette 31 is provided by a hopping roller 32 provided at the front end of the paper feed cassette 31. Sheets are fed one by one from 31 and sent to image forming units Bk, Y, M, and C via conveying rollers 33 and 34.

  A fixing device 35 as a fixing device is disposed downstream of the image forming units Bk, Y, M, and C in the paper transport direction. The fixing device 35 includes a fixing roller r1 as a heating roller and a pressure roller r2 as a pressure roller. In the fixing device 35, a color toner image is fixed on a sheet to form a color image. Is done. The sheet on which the color image is formed is discharged out of the main body of the printer, that is, the apparatus main body by the discharge roller 36.

  Next, the developing device 20 will be described.

  The developing device 20 includes a developing belt unit 16, a toner supply roller 18 as a developer supplying member, a developing blade 17 as a developer layer regulating member, and the like. In the present embodiment, the first to third rollers 161 to 163 and the developer carrying member stretched by the first to third rollers 161 to 163 A developing belt 164 is provided.

  The toner supply roller 18 is disposed between the first roller 161 and the third roller 163 in contact with the developing belt 164 with a predetermined nip pressure, and is rotated in the direction of the arrow b so that the toner 14 The developing blade 17 is disposed in contact with the developing belt 164 so as to face the first roller 161 and form a thin layer of the toner 14 on the developing belt 164.

  The developing belt 164 is disposed so as to be opposed to the photosensitive drum 11 between the first roller 161 and the second roller 162, and in this embodiment, the developing belt 164 is disposed. The upper toner 14 is adhered to the photosensitive drum 11. In the present embodiment, the developing belt 164 is disposed in contact with the photosensitive drum 11, but may be disposed opposite to the photosensitive drum 11.

  The first roller 161 functions as a drive roller, is rotated by a rotation of a drive motor (not shown) as a drive unit, and causes the developing belt 164 to travel in the direction of arrow c. The second and third rollers 162 and 163 function as driven rollers, and are driven and rotated as the developing belt 164 travels. For this purpose, one of the second and third rollers 162 and 163 is urged in a direction away from the first roller 161 by a coil spring (not shown) as an urging member and is applied to the developing belt 164. A predetermined tension is applied. The developing belt 164 is caused to run in the opposite direction to the rotation direction of the photosensitive drum 11 and in the same direction as the rotation direction of the toner supply roller 18.

  In the present embodiment, the first roller 161 is caused to function as a driving roller, but the second roller 162 can also be functioned as a driving roller, or the third roller 163 can be functioned as a driving roller. .

The toner supply roller 18 is formed by coating an elastic layer around a metal shaft. The elastic layer is formed of urethane resin, polyimide resin, polyimide amide resin, urethane rubber, chloroprene rubber, silicone rubber, etc., and has a volume resistivity of 10 ⁷ [Ωcm] or more and 10 ⁹ [Ωcm] or less, The surface roughness Rz is set to 5 [μm] or more and 30 [μm] or less.

  The developing blade 17 has elasticity and is made of a thin metal plate having a thickness of 0.2 mm or more and 1.5 mm or less. The tip of the developing blade 17 is bent, and the developing belt 164 is formed. Is pressed at a predetermined pressure.

The developing belt 164 is made of chloroprene rubber or the like, and has a volume resistivity of 10 ⁵ [Ωcm] or more and 10 ⁸ [Ωcm] or less. When the volume resistivity of the developing belt 164 is less than 10 ⁵ [Ωcm], a current flows on the developing belt 164 due to the voltage applied to the second and third rollers 162 and 163. On the other hand, when the volume resistivity of the developing belt 164 is larger than 10 ⁸ [Ωcm], it becomes difficult to form a potential gradient by resistance division, which will be described later, as desired. Further, the surface roughness Rz of the developing belt 164 is 2 [μm] or more and 15 [μm] or less.

The developing belt 164 can be formed of a semiconductive urethane resin other than chloroprene rubber, polyimide resin, polyimide amide resin, urethane rubber, silicone rubber, NBR rubber, or the like. Similarly, the developing belt 164 The volume resistivity is 10 ⁵ [Ωcm] or more and 10 ⁸ [Ωcm] or less, and the surface roughness Rz is 2 [μm] or more and 15 [μm] or less.

  The developing belt 164 has a length of the contact portion, that is, a nip width of 2 [in a contact portion (nip portion) set at a predetermined position between the first roller 161 and the third roller 163. mm] or more and 20 [mm] or less. If the nip width is less than 2 [mm], it is not possible to sufficiently secure a potential difference between a contact start portion R2 and a contact end portion S2 described later. On the other hand, when the nip width is larger than 20 [mm], the load due to the frictional resistance between the developing belt 164 and the toner supply roller 18 is increased, and the toner 14 is significantly deteriorated.

  As the first roller 161 rotates, the developing belt 164 contacts the photosensitive drum 11 at a facing portion D2 set at a predetermined position between the first roller 161 and the second roller 162. In the direction of the arrow c at a peripheral speed that is in contact with the photosensitive drum 11 in a direction opposite to the rotation direction of the photosensitive drum 11 and that is 1.1 times or more and 1.3 times or less the circumferential speed of the photosensitive drum 11. It is made to run.

  Further, the developing belt 164 moves away from the third roller 163 at the separation portion R1 as it travels, contacts the first roller 161 at the contact portion S1, and contacts between the separation portion R1 and the contact portion S1. The contact with the toner supply roller 18 is started at the contact start portion R2, and the contact with the toner supply roller 18 is ended at the contact end portion S2.

  That is, the developing belt 164 is brought into contact with the toner supply roller 18 from the contact start portion R2 to the contact end portion S2. The contact start portion R2 is at the upstream end of the contact portion in the traveling direction of the developing belt 164, and the contact end portion S2 is downstream of the contact portion in the traveling direction of the developing belt 164. Formed at the end of each.

  In the present embodiment, the first roller 161 is formed by coating a conductive elastic layer around a metal shaft in order to increase the running performance of the developing belt 164. Besides covering the elastic layer, the shaft can be subjected to sandblasting, knurling or the like.

  In the present embodiment, the toner 14 is a one-component toner, and includes a toner main body made of a resin component such as polyester and polystyrene, a colorant, a release agent, a charge control agent, and the like, and the toner main body. It consists of an external additive such as silica added to the surface layer, and is formed by a pulverization method or a polymerization method. The toner 14 has a volume average particle size of 3 [μm] or more and 10 [μm] or less, and an average sphericity φ of 0.90 or more and 0.98 or less.

The average sphericity φ of the toner 14 is measured using a flow type particle image analyzer (manufactured by Toa Medical Electronics Co., Ltd., FPIA-2000), and the total sphericity of the measured toner particles is measured. It is calculated by dividing by the number of toner particles (the number of toner detection particles is 3500). The sphericity is an index indicating the degree of unevenness of the toner 14,
Sphericity = (diameter of the circle equal to the projected particle area)
/ (Diameter of the smallest circle circumscribing the particle projection image)
It is represented by The particle projected area is a binarized toner particle image area. When the toner 14 is a perfect sphere, the sphericity is 1.00, and becomes smaller as the surface shape becomes more complicated.

  Further, the toner 14 has a charge amount of −60 [μQ / m] or more and −20 [μQ / m] or less when measured by the blow-off method by adding a charge control agent, an external additive, or the like. It is adjusted to become.

The first roller 161 is supplied with the voltage VD1 by the high-voltage power supply 41, the second roller 162 is supplied with the voltage VD2 by the high-voltage power supply 42, the third roller 163 is supplied with the voltage VR by the high-voltage power supply 43, and the toner supply roller 18 The voltage VS is applied to the high voltage power supply 44. Each voltage VD1, VD2, VR, VS has the same polarity, and the absolute value of each voltage VD1, VD2, VR, VS is
| VD1 | = | VD2 | <| VS | <| VR |
To be.

  Next, the operation of the printer having the above configuration will be described.

  First, when an image forming operation is started, the drive motor is driven, and the photosensitive drum 11, the first roller 161, and the toner supply roller 18 are rotated. Accordingly, the toner 14 supplied from the toner cartridge 13 adheres to the surface of the toner supply roller 18 and is conveyed, and contacts the developing belt 164 at the contact end portion S2.

By the way, in this embodiment, the voltage VD1 and the voltage VD2 are set to -200 [V], the voltage VR is set to -500 [V], and the voltage VS is set to -350 [V]. Further, in the direction opposite to the traveling direction of the developing belt 164, the distance L1 from the contact portion S1 to the separation portion R1 is 12 [mm], and the distance L2 from the contact portion S1 to the contact end portion S2 is 2. When the distance L3 from the contact end portion S2 to the contact start portion R2 is 8 [mm] and the distance L4 from the contact start portion R2 to the separation portion R1 is 2 [mm],
L1 = L2 + L3 + L4
become.

  Further, the developing belt 164 has a thickness of 1 [mm], the outer diameter of the photosensitive drum 11 is 30 [mm], and the first to third rollers 161 to 163 have an outer diameter of 6 [mm]. The outer diameter of the supply roller 18 is 15 [mm].

  Next, the relationship between the distance from the contact portion S1 in the direction opposite to the traveling direction of the developing belt 164 and the potential formed on the developing belt 164 will be described.

  FIG. 4 is a diagram showing the relationship between the distance from the contact portion and the potential formed on the developing belt in the first embodiment of the present invention. In the figure, the horizontal axis represents distance and the vertical axis represents potential.

  As described above, since the voltage VD1 is applied to the first roller 161 and the voltage VR is applied to the third roller 163, the contact end portion S2 includes the contact end portion from the contact portion S1. A potential V1 obtained by resistance-dividing the potential difference between the voltage VD1 and the voltage VR is formed by the distance L2 to S2 and the distance (L3 + L4) from the contact end portion S2 to the separation portion R1, and the contact start portion R2 includes A potential V2 obtained by resistance-dividing the potential difference between the voltage VD1 and the voltage VR is formed by the distance (L2 + L3) from the contact portion S1 to the contact start portion R2 and the distance L4 from the contact start portion R2 to the separation portion R1. The

The potential difference VT between the voltage VD1 and the voltage VR is
VT = −500 − (− 200)
= -300 [V]
Therefore, the potential V1 formed at the contact end portion S2 is
V1 = −200 + (− 300) × (2/12)
= -250 [V]
become.

The potential V2 formed at the contact start portion R2 is
V2 = −500 − (− 300) × (2/12)
= -450 [V]
become.

  In this case, the potential V1 of the contact end portion S2 has the same polarity as the voltage VS (−350 [V]) applied to the toner supply roller 18 and has an absolute value smaller than the voltage VS (| V1 | <| VS |), an electric field for moving the toner 14 charged with negative polarity from the toner supply roller 18 to the developing belt 164 is formed in the contact end portion S2, and the toner 14 is developed by the electric field. The belt is moved to the belt 164 and attached to the developing belt 164. The toner 14 attached to the developing belt 164 is transported as the developing belt 164 travels, and is formed into a uniform thin layer when passing through the developing blade 17.

Further, since the voltage VD1 and the voltage VD2 have the same polarity and value, the separation portion D1 where the developing belt 164 is separated from the first roller 161 and the contact portion D3 where the developing belt 164 is in contact with the second roller 162 In the meantime, the potential formed on the developing belt 164 becomes −200 [V]. Therefore, the potential V3 formed at the facing portion D2 is
V3 = -200 [V]
become.

  In this case, the potential V3 becomes a value suitable for developing the electrostatic latent image on the photosensitive drum 11 by reversal development, and the toner 14 on the developing belt 164 adheres to the photosensitive drum 11 at the facing portion D2. Be made. That is, the potential V3 formed at the facing portion D2 is −200 [V], and the potential of the portion where the electrostatic latent image is formed on the surface of the photosensitive drum 11 is −50 [V]. Since the potential of the portion where the electrostatic latent image is not formed on the surface of the drum 11 is −600 [V], the toner 14 charged to a negative polarity is attached to the portion where the electrostatic latent image is not formed. Instead, it adheres to the portion where the electrostatic latent image is formed. In this way, the electrostatic latent image can be developed. Further, the toner 14 that is not used for development and remains on the developing belt 164 is moved to the toner supply roller 18 at the contact start portion R2 as the developing belt 164 travels.

  By the way, as described above, the potential V2 is formed in the contact start portion R2. The potential V2 has the same polarity as the voltage VS (−350 [V]) applied to the toner supply roller 18 and has an absolute value larger than the voltage VS (| V2 |> | VS |). In the contact start portion R2, an electric field for moving the toner 14 charged to a negative polarity to the toner supply roller 18 is formed, and the toner 14 is moved from the developing belt 164 to the toner supply roller 18 by the electric field. Collected.

  Thereafter, the recovered toner 14 is conveyed along with the rotation of the toner supply roller 18 together with the toner 14 newly supplied from the toner cartridge 13, and is sent to the contact end portion S2, and as described above, the contact At the end S <b> 2, the belt is moved to the developing belt 164 and attached again to the developing belt 164.

  In this manner, the supply of the toner 14 from the toner supply roller 18 to the developing belt 164 at the contact end portion S2 and the recovery of the toner 14 from the developing belt 164 to the toner supply roller 18 at the contact start portion R2 are repeatedly performed. Is called.

  As described above, in the present embodiment, the developing belt 164 is stretched by the first to third rollers 161 to 163, and the developing belt 164 and the photosensitive drum are interposed between the first and second rollers 161 and 162. 11, the developing belt 164 and the toner supply roller 18 are contacted between the first and third rollers 161 and 163, and a predetermined distance is provided between the developing belt 164 and the toner supply roller 18. Thus, different potentials can be formed at the contact start portion R2 and the contact end portion S2.

  Accordingly, an electric field for supplying the toner 14 from the toner supply roller 18 to the developing belt 164 and an electric field for recovering the toner 14 from the developing belt 164 to the toner supplying roller 18 can be formed. The toner 14 remaining on 164 is sufficiently scraped off by the toner supply roller 18 and does not adhere to the photosensitive drum 11 as it is in the next development process. As a result, afterimages can be prevented from being formed on the paper, and the image quality can be improved.

  Further, since different voltages VD2 and VR are applied to the second and third rollers 162 and 163, the potentials V1, V2 and V3 formed at the contact end portion S2, the contact start portion R2 and the facing portion D2, respectively. Can be set to various values, and the degree of freedom in designing the developing device 20 can be increased.

  Further, since the nip width is formed by bringing the photosensitive drum 11 and the toner supply roller 18 into contact with the developing belt 164, the nip pressure can be lowered. Accordingly, it is possible to suppress the deterioration of the respective members such as the photosensitive drum 11, the toner supply roller 18, the developing belt 164, and the deterioration of the toner 14.

  Since the voltage VD1 and the voltage VD2 have the same polarity and value, the potential formed on the developing belt 164 between the separation part D1 and the contact part D3 is constant, and becomes −200 [V]. Therefore, the potential V3 formed at the facing portion D2 is the same as −200 regardless of where the developing belt 164 and the photosensitive drum 11 are brought into contact with each other between the separation portion D1 and the contact portion D3. [V]. As a result, the position of the facing portion D2 can be easily set, and the degree of freedom in designing the developing device 20 can be further increased.

  Next, a second embodiment of the present invention will be described. The structure of the printer in this embodiment is the same as that of the printer in the first embodiment, and will be described with reference to FIGS. Moreover, about the thing which has the same structure as 1st Embodiment, the same code | symbol is provided and the effect of the same embodiment is used about the effect of the invention by having the same structure.

In this case, the voltage VD1 applied to the first roller is +50 [V], the voltage VD2 applied to the second roller is -450 [V], and the voltage VR applied to the third roller is- At 250 [V], the voltage VS applied to the toner supply roller 18 as the developer supply member is set to −100 [V]. The voltage VD1 has a polarity opposite to that of the voltages VD2, VR, VS, and the absolute values of the voltages VD2, VR, VS are:
| VS | <| VR | <| VD2 |
To be.

Further, in the direction opposite to the traveling direction of the developing belt 164 as the developer carrier, the distance L1 from the contact portion S1 to the separation portion R1 is set to 12 [mm], and the contact end portion S1 to the contact end portion S2. The distance L2 from the contact end portion S2 to the contact start portion R2 is set to 8 [mm], and the distance L4 from the contact start portion R2 to the separation portion R1 is set to 2 [mm]. ]
L1 = L2 + L3 + L4
become.

  Accordingly, since the voltage VD1 is applied to the first roller 161 and the voltage VR is applied to the third roller 163, the distance from the contact portion S1 to the contact end portion S2 is set in the contact end portion S2. A potential V1 obtained by resistance-dividing the potential difference between the voltage VD1 and the voltage VR is formed by L2 and the distance (L3 + L4) from the contact end portion S2 to the separation portion R1, and the contact start portion R1 has a contact portion S1. A potential V2 obtained by resistance-dividing the potential difference between the voltage VD1 and the voltage VR is formed by the distance (L2 + L3) from the contact start portion R2 to the contact start portion R2 and the distance L4 from the contact start portion R2 to the separation portion R1.

The potential difference VT between the voltage VD1 and the voltage VR is
VT = −250 − (+ 50)
= -300 [V]
Therefore, the potential V1 formed at the contact end portion S2 is
V1 = 50 + (− 300) × (2/12)
= 0 [V]
become.

The potential V2 formed at the contact start portion R2 is
V2 = −250 − (− 300) × (2/12)
= -200 [V]
become.

  In this case, the potential V1 of the contact end portion S2 has the same polarity as the voltage VS (−100 [V]) applied to the toner supply roller 18, and has an absolute value smaller than the voltage VS (| V1 | <| VS |), an electric field for moving the toner 14 as the developer charged to a negative polarity from the toner supply roller 18 to the developing belt 164 is formed in the contact end portion S2, and the electric field is generated by the electric field. The toner 14 is moved to the developing belt 164 and attached to the developing belt 164. The toner 14 adhering to the developing belt 164 is conveyed as the developing belt 164 travels, and is formed into a uniform thin layer when passing through the developing blade 17 as a developer layer regulating member.

By the way, when the facing portion D2 between the developing belt 164 and the photosensitive drum 11 as the image carrier is set at the center of the distance between the first and second rollers 161 and 162, the facing portion D2 on the developing belt 164 is formed. The potential V3 to be applied is
V3 = 50 + (− 450) × (1/2)
= -200 [V]
become.

  In this case, the potential V3 becomes a value suitable for developing the electrostatic latent image as the latent image on the photosensitive drum 11 by reversal development, and the toner 14 on the developing belt 164 is transferred to the photosensitive member at the facing portion D2. Attached to the drum 11. That is, the potential V3 formed at the facing portion D2 is −200 [V], and the potential of the portion where the electrostatic latent image is formed on the surface of the photosensitive drum 11 is −50 [V]. Since the potential of the portion where the electrostatic latent image is not formed on the surface of the drum 11 is −600 [V], the toner 14 charged to a negative polarity is attached to the portion where the electrostatic latent image is not formed. Instead, it adheres to the portion where the electrostatic latent image is formed. In this way, the electrostatic latent image can be developed. Further, the toner 14 that is not used for development and remains on the developing belt 164 is moved to the toner supply roller 18 at the contact start portion R2 as the developing belt 164 travels.

  By the way, as described above, the potential V2 is formed in the contact start portion R2. The potential V2 has the same polarity as the voltage VS (−100 [V]) applied to the toner supply roller 18 and has an absolute value larger than the voltage VS (| V2 |> | VS |). In the contact start portion R2, an electric field for moving the toner 14 charged to a negative polarity to the toner supply roller 18 is formed, and the toner 14 is moved from the developing belt 164 to the toner supply roller 18 by the electric field. Collected.

  Thereafter, the recovered toner 14 is conveyed along with the rotation of the toner supply roller 18 together with the toner 14 newly supplied from the toner cartridge 13 as a developer container and as a developer cartridge, and the contact is completed. As described above, it is moved to the developing belt 164 and is attached to the developing belt 164 again at the contact end portion S2.

  In this manner, the supply of the toner 14 from the toner supply roller 18 to the developing belt 164 at the contact end portion S2 and the recovery of the toner 14 from the developing belt 164 to the toner supply roller 18 at the contact start portion R2 are repeatedly performed. Is called.

  The first roller 161 can be grounded and the voltage VD1 can be set to 0 [V]. In this case, when the voltage VD2 is set to -400 [V], the voltage VR is set to -300 [V], and the voltage VS is set to -150 [V], the potential V1 of the contact end portion S2 is set to -50 [V]. Become. The potential V1 of the contact end portion S2 has the same polarity as the voltage VS (−150 [V]) applied to the toner supply roller 18 and has an absolute value smaller than the voltage VS (| V1 | < | VS |), an electric field for moving the negatively charged toner 14 from the toner supply roller 18 to the developing belt 164 is formed in the contact end portion S2. Further, the potential V2 at the contact start portion R2 becomes −350 [V].

  When the facing portion D2 between the developing belt 164 and the photosensitive drum 11 is set at the center of the distance between the first and second rollers 161 and 162, the potential V3 formed at the facing portion D2 on the developing belt 164 is , −200 [V]. In this case, the potential V3 becomes a value suitable for developing the electrostatic latent image on the photosensitive drum 11 by reversal development, and the toner 14 on the developing belt 164 adheres to the photosensitive drum 11 at the facing portion D2. Be made.

  Further, the potential V2 of the contact start portion R2 becomes −350 [V], has the same polarity as the voltage VS (−150 [V]) applied to the toner supply roller 18, and is absolute from the voltage VS. Since the value is large (| V2 |> | VS |), an electric field for moving the toner 14 charged to the negative polarity to the toner supply roller 18 is formed in the contact start portion R2, and the toner is generated by the electric field. 14 is moved from the developing belt 164 to the toner supply roller 18 and collected.

  In each of the above embodiments, an electrophotographic color printer has been described. However, the present invention can be applied to a monochrome printer. The present invention can also be applied to a copying machine, a facsimile machine, a multifunction machine, and the like.

  The present invention is not limited to the above embodiments, and various modifications can be made based on the gist of the present invention, and they are not excluded from the scope of the present invention.

11 Photosensitive drum 14 Toner 18 Toner supply roller 20 Developer 161 First roller 162 Second roller 163 Third roller 164 Developing belt D2 Opposing portion

Claims (9)

(A) a first roller;
(B) a second roller;
(C) a third roller;
(D) a developing belt that is stretched by the first to third rollers and is caused to travel as rotation is transmitted to a predetermined roller among the first to third rollers;
(E) The developing belt is opposed to the image carrier at a facing portion set at a predetermined position between the first and second rollers, and is set at a predetermined position between the first and third rollers. In contact with the developer supply member at the contact portion,
(F) In the facing portion, the developer on the developing belt is attached to the image carrier,
(G) In the contact portion, the developer is supplied from the developer supply member to the development belt, and the developer is collected from the development belt to the developer supply member.   2. The developing device according to claim 1, wherein a potential for attaching a developer to a portion where an electrostatic latent image is formed on the surface of the image carrier is formed on the developing belt in the facing portion. (A) a contact start portion is formed at an upstream end portion of the contact portion in the running direction of the developing belt, and a contact end portion is formed at a downstream end portion;
(B) The developer is supplied from the developer supply member to the developing belt at the contact end portion, and the developer is collected from the developing belt to the developer supply member at the contact start portion. The developing device described. (A) a potential having the same polarity as the voltage applied to the developer supply member and having an absolute value smaller than the voltage applied to the developer supply member is formed at the contact end portion;
(B) A potential having the same polarity as a voltage applied to the developer supply member and having an absolute value larger than a voltage applied to the developer supply member is formed at the contact start portion. Item 4. The developing device according to Item 3.   The developing device according to claim 1, wherein voltages having the same polarity and value are applied to the first and second rollers. When the voltage applied to the first roller is VD1, the voltage applied to the third roller is VR, and the voltage applied to the developer supply member is VS,
(A) Each voltage VD1, VR, VS has the same polarity,
(B) The absolute values of the voltages VD1, VR, VS are
| VD1 | <| VS | <| VR |
The developing device according to claim 1, wherein the developing device is used. When the voltage applied to the first roller is VD1, the voltage applied to the third roller is VR, and the voltage applied to the developer supply member is VS,
(A) The voltage VD1 has a polarity opposite to that of each of the voltages VR and VS,
(B) The absolute values of the voltages VR and VS are
| VS | <| VR |
The developing device according to claim 1, wherein the developing device is used. When the voltage applied to the first roller is VD1, the voltage applied to the third roller is VR, and the voltage applied to the developer supply member is VS,
(A) The voltage VD1 is set to 0 [V],
(B) Each voltage VR, VS has the same polarity,
(C) The absolute values of the voltages VR and VS are
| VS | <| VR |
The developing device according to claim 1, wherein the developing device is used.   An image forming apparatus equipped with the developing device according to claim 1.

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